2.5 - biological membranes *

Question 1

what are biological membranes described as and why?

Answer 1

• fluid mosaic model
• due to mixture + movement of the phospholipids, proteins, glycoproteins, and glycolipids it’s made of

Question 2

why is cholesterol present in some membranes?

Answer 2

• restricts lateral movement of other molecules in the membrane
• useful as makes membrane less fluid at high temperatures + prevents water and dissolved ions leaking out of cell

Question 3

how is the phospholipid bilayer of a membrane formed?

Answer 3

align as hydrophilic heads attracted to water and the hydrophobic tails repelled by water

Question 4

what is present in a biological membrane?

Answer 4

phospholipid bilayer, glycoprotein, glycolipid, peripheral membrane protein, integral membrane protein, channel protein + often cholesterol

Question 5

what are peripheral membrane proteins and what do they do?

Answer 5

• do not extend completely across membrane
• either provide mechanical support or are connected to proteins or lipids to make glycoproteins and glycolipids
• their function is cell recognition as receptors

Question 6

what are integral membrane proteins?

Answer 6

• span across from one side of the bilayer to another
• protein carriers or channel proteins involved in the transport of molecules across the membrane

Question 7

difference between protein channels and carrier proteins?

Answer 7

• protein channels form tubes that fill with water to enable water-soluble ions to diffuse
• carrier proteins bind with other ones and larger molecules, such as glucose and amino acids, and change shape to transport them to the other side of the membrane

Question 8

describe simple diffusion?

Answer 8

• net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached
• process does not require ATP
• molecules must be lipid-soluble and small

Question 9

describe facilitated diffusion?

Answer 9

• high to low concentration
• passive so doesn’t require ATP
• for molecules that are either too large or insoluble

Question 10

what is osmosis?

Answer 10

movement of water from area of higher water potential to area of lower water potential across a partially permeable membrane

Question 11

what is water potential?

Answer 11

• pressure created by water molecules and is measured in Pa and represented with the symbol Ψ
• pure water has water potential of zero, so when solutes are dissolved in water, the water potential will become negative
• the more negative the water potential, the more solute must be dissolved in it

Question 12

what is an isotonic solution?

Answer 12

when the water potential is the same in the solution and the cell within the solution

Question 13

what is a hypotonic solution?

Answer 13

when the water potential of a solution is more positive (closer to zero) than the cell

Question 14

what is a hypertonic solution?

Answer 14

when the water potential of a solution is more negative than the cell

Question 15

what happens to animal and plant cells if placed in hypotonic solution?

Answer 15

animal = a lot of water will move into the cell by osmosis and as animal cells do not have a cell wall, the pressure will cause the cell to burst

plant = do not burst because of the strengthened cell wall

Question 16

what will happen to animal and plant cells if placed in hypertonic solution?

Answer 16

both will shrink and become shrivelled due to large volumes of water leaving the cell by osmosis

Question 17

describe active transport?

Answer 17

• movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins
• selective as only certain molecules can bind to receptor site on carrier proteins

Question 18

example of co transport and how it works?

Answer 18

• the absorption of sodium and glucose ions from the small intestines specifically the ileum
• sodium ions must be transported by active transport from the epithelial cells to the blood via a protein carrier
• this lowers the concentration of sodium in the epithelial cell to create a concentration gradient between the ileum and the epithelial cell
• sodium ions diffuse into the epithelial cell down the concentration gradient. This is through a co-transport protein
• sodium ions bind and diffuse through the co-transport carrier protein, either glucose or amino acids can be transported into the epithelial cells with them

Question 19

adaptations to maximise transport?

Answer 19

• a larger surface area, a higher number of channel/carrier proteins, and a steeper concentration gradient, the rate of transport will be increased
• microvilli in the ileum, for example, are finger-like projections that increase the surface area and contain many protein carriers and channels to maximize the absorption of digested food
• network of capillaries so that all absorbed molecules are transported away in the blood immediately to ensure a concentration gradient is maintained

Question 20

what is passive transport?

Answer 20

• high to low water potential and concentration
• H2O travelling through phospholipid bilayer
• small particles like CO2 and O2

Question 21

what is exocytosis and endocytosis?

Answer 21

exo = removing products from cell

endo = ingesting products into cell

Question 22

what is pinocytosis and phagocytosis?

Answer 22

pino = ingestion of fluids around cell

phago = ingestion of solids around cell